d and e are incorrect because * indicates a default candidate but
since its a nssa area not nssa nosummary there will be no default
candidate as type 1 to 4 are allowed and type 5 is replaced by type 7.

Yes, I mis-spoke about LSA 4, they are indeed allowed under NSSA. A,B,C is
likely the expected answer. However, O*N2 doesn't require NO-SUMMARY and is
thus supported under NSSA. Since LSA 4s are not blocked, O*N2 would
probably not considered in the top 3 answers.